The use of organic polymers in numerous applications has grown in recent years to the degree that rigid polymers such as nylons and polyacetal resins have almost replaced more conventional metal, wood, and ceramic materials. The development of low cost and efficient methods of preparing polyolefin resins has made them excellent candidates for a wider range of applications provided that certain physical properties such as clarity, hardness, warping and crystallization rates can be improved.
In recent years, much research has been conducted in the field to develop various methods and/or catalysts for improving the physical properties of polyolefin polymers. A vast majority of this research has been directed towards filling polyolefins with finely divided solids or fibrous fillers. One such method of providing filled polyolefins is by melt mixing the polyolefin with a filler material such as talc. This procedure, however, requires that the polyolefin be of relatively low molecular weight, that is, have an inherent viscosity less than about 2. While the resulting polymeric products produced by this method may generally have some improved physical properties, they do suffer from the disadvantage of having a slow crystallization rate.
Furthermore, serious problems of compounding these polymers, prepared by melt mixing with talc, are encountered as manifested by high power required in operating mixing machinery, heat degradation of polymer, nonuniformity of talc dispersion and poor adhesion of the polymer to talc, even when coupling agents are employed.
Recently, various methods have been proposed and developed to decrease the problems mentioned above, the most widely of which is the polymerization of the olefin in the presence of selected fillers such as talc. One suggested method of effecting olefin polymerization in the presence of the filler is by employing a coordination catalyst. In this method, well-known coordination catalysts comprising the combination of a transition metal halide, an ester and a reducing compound, such as an organometallic compound of a metal of Group Ia, IIa or IIIa of the Periodic Table of Elements, are generally employed.
Another method of improving the physical properties of polyolefins using a filler material such as talc is disclosed in U.S. Pat. No. 3,950,303 to Lipscomb. This reference describes a process of polymerizing olefins onto a chromium-modified filler in the presence of an organometallic compound. Moreover, the process disclosed by Lipscomb involves (a) contacting an inorganic filler material with a solution of a chromium(III) compound whereby the chromium compound is adsorbed onto the surface of the filler; (b) activating the chromium-modified filler by drying; (c) dispersing the filler as a slurry in an inert, liquid hydrocarbon; (d) adding an organoaluminum compound to said slurry; and (e) polymerizing an olefin in said slurry. This method is said to result in the formation of an essentially homogeneous, filled polyolefin composition having a good combination of hardness, toughness and stiffness.
U.S. Pat. No. 4,104,243 to Howard, Jr. relates to a process for preparing low viscosity inorganic filler compound dispersions and the use of the same in the preparation of polyolefin/inorganic filler compositions. More specifically, the process as described in the reference involves dispersing a large amount of a finely divided inorganic filler compound as a slurry in an inert hydrocarbon diluent in the presence of an organoaluminum compound. This slurry is then contacted with a Ziegler-type catalyst and an olefin to produce a polyolefin/filler composition.
U.S. Pat. No. 4,473,672 to Bottrill relates to a process of producing a polymer composition which is a composite material containing an olefin polymer and a filler. Moreover, the patentee discloses a polymer composite which is produced by polymerizing an olefin monomer in the presence of a catalyst system obtained by reacting a filler material with (a) an organic magnesium compound which contains a halogen or (b) an organomagnesium compound and thereafter with a halogen-containing compound; and then treating that reaction product with a transition metal compound, which is preferably TiCl.sub.4, and an organic activating compound. The resultant homogeneous composites are said to have good flow characteristics.
The method disclosed by Bottrill, however, suffers from the disadvantage that the composite will contain a halogen, therefore, it is necessary to carry out a deashing step. The use of a deashing step is undesirable since those skilled in the art are aware that halogens can adversely affect the polymer product as well as cause corrosion of the machinery used to process the final product.
One such method of overcoming the deashing problem described above is disclosed in U.S. Pat. No. 4,564,647 to Hayashi et al. which describes a process for producing a polyethylene composition which comprises polymerizing ethylene in the presence of a catalyst comprising a contact treatment product of a high activity catalyst component, a filler and an organoaluminum compound. This process does not require a deashing step since the catalyst employed has remarkably high activity although containing very little halogen.
Japanese Patent No. 63-256603 provides a highly crystalline polypropylene resin which is prepared by polymerizing propylene in the presence of a catalyst system comprising a solid transition metal catalyst that is prepared by supporting a titanium halide on a carrier comprising talc and a magnesium halide wherein the weight of talc to magnesium halide is in the range of between 1:1000 and 1:1. This correlates to a range of talc to magnesium in the magnesium halide of between 1:3915 to 1:3.9.
Despite the current state of the art, there still exists a need to develop new solid catalyst components which, when used in conjunction with suitable cocatalysts, provide polyolefin resins that have improved physical properties as well as having a uniform dispersion of a filler, such as talc, dispersed in the resin.